Disordered magnetic ground state in a quasi-1-Dd4columnar iridate Sr3LiIrO6.

Spin-orbit coupling offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise 'ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2Hspin-chaind4iridate Sr3LiIrO6with geometric frustration. Our structural studies reveal Li-Ir chemical order with desired stoichiometry in this compound, while x-ray absorption together with x-ray photoemission spectroscopic characterizations establish pure 5+ valence of Ir. We have established a magnetic ground state with finite Ir5+magnetic moments in this compound, contrary to the anticipated nonmagneticJeff= 0 state, through combined dc susceptibility,7Li nuclear magnetic resonance (NMR), muon spin relaxation (µSR) andab-initioelectronic structure studies. These investigations together with ac magnetic susceptibility and specific heat measurements reveal that despite having noticeable antiferromagnetic correlation among the Ir5+local moments, this system does not magnetically order down to at least 0.05 K, possibly due to geometrical exchange frustration, arising from the comparable nearest- and next-nearest-neighbor interchain Ir-O-O-Ir superexchange interaction strengths with opposite signs. However, the zero-fieldµSR analysis shows emergence of a considerable proportion of spin-freezing on top of a spin-fluctuating dynamic magnetic background down to the lowest measured temperature of 1.7 K, possibly due to some inhomogeneity and/or the much stronger intra-column Ir-Ir magnetic exchange interaction strength relative to the inter-column Ir-Ir ones. The linear temperature dependence of the magnetic specific heat (Cm) in both zero and applied magnetic fields, plus the power-law behavior of the NMR spin-lattice relaxation rate suggest a gapless spinon density of states in this charge gapped disordered magnetic ground state of Sr3LiIrO6.

Observation of an exotic insulator to insulator transition upon electron doping the Mott insulator CeMnAsO.

A promising route to discover exotic electronic states in correlated electron systems is to vary the hole or electron doping away from a Mott insulating state. Important examples include quantum criticality and high-temperature superconductivity in cuprates. Here, we report the surprising discovery of a quantum insulating state upon electron doping the Mott insulator CeMnAsO, which emerges below a distinct critical transition temperature, TII. The insulator-insulator transition is accompanied by a significant reduction in electron mobility as well as a colossal Seebeck effect and slow dynamics due to decoupling of the electrons from the lattice phonons. The origin of the transition is tentatively interpreted in terms of many-body localization, which has not been observed previously in a solid-state material.

Multiple magnetic-phase transitions and critical behavior of charge-density wave compound TbTe3.

We report multiple magnetic phase transitions and critical behavior of the 2D charge-density wave compound TbTe3 studied by µSR measurements and dc magnetization measurements. Zero-field µSR has shown three magnetic transitions below 7 K. The longitudinal field measurements under 50 G has confirmed the first transition at T N = 6.3 K. Scaling analysis from above T N gives the critical exponent w = 0.63(5), suggesting the Ising 3D antiferromagnetic nature of the ordering, which is likely mediated by the 2D correlations. However, the obtained w = 0.81(5) below T N indicates the ferromagnetic phase, which arises over the multiphase transitions at lower temperatures. Temperature-dependent transverse frequency shift gives a relatively smaller exponent γ = 1.0(1) than the Ising 3D model. The different transitions were also observed by dc magnetization measurements, suggesting two magnetic transitions at 7.4 K and 3.1 K, which correspond to the antiferromagnetic and ferromagnetic phases respectively.

The suppression of CMR in Nd(Mn1-xCox)AsO0.95F0.05.

The colossal magnetoresistance (CMR) observed in the oxypnictide NdMnAsO1-xFx has been further investigated. The magnetotransport is dominated by magnetopolarons. Magnetoresistance measurements of the series Nd(Mn1-xCox)AsO0.95F0.05 show that doping with cobalt on the manganese site pins the magnetopolarons and suppresses the CMR, which is completely destroyed by x = 0.047. The chemical doping results in non-stoichiometric samples, with both As and O vacancies. The relationship between the non-stoichiometry, magnetic order, electron doping and CMR is explored. The Nd antiferromagnetic transition and simultaneous reorientation of the Mn spins into the basal plane at 23 K (TSR) is not effected by Co doping. However, there is a significant decrease in TN(Mn) as the antiferromagnetic transition is suppressed from 360 K to 300 K as x increases from 0-0.047. The manganese moment at 10 K is also reduced from 3.86(2)µB to 3.21(2)µB over the same doping range. This reduction in the in-plane Mn moment decreases the electron-electron correlations below TSR and acts to further diminish the magnetoresistance.

Magnetic and structural changes in LaCo0.9Mn0.1O3 at high pressure.

The structural and magnetic properties of LaCo0.9Mn0.1O3 have been studied as a function of pressure by neutron powder diffraction and DC magnetometry. The material is confirmed to exhibit rhombohedral R [Formula: see text] c symmetry between ambient pressure and 6 GPa. We have determined the bulk modulus B 0 of the sample using a second-order Birch-Murnaghan equation of state which yielded: B 0 = 140(9) GPa and V [Formula: see text]. We report a non-linear increase of the Curie temperature T C from an ambient pressure value of 224.7 K to ∼236 K at a pressure of 4 GPa. Finally, we confirm the glassy-like nature of the magnetism in LaCo0.9Mn0.1O3, which is maintained throughout the pressure range explored.

Inter and intra macro-cell model for point dipole-dipole energy calculations.

In the field of micromagnetics, the calculation of long-range dipole-dipole interactions in non-uniformly magnetized bodies has long posed computational problems. In this paper, we present an inter and intra macro-cell point-dipole model, which can be used to speed-up the determination of dipole-dipole energies at the atomistic level. The model can be used to accurately compute the dipole-dipole energy, using macro-cells of any shape or size.

New insights into the phase diagram of a magnetic perovskite, LaCo1/3Mn2/3O3.

We report the crystal structure of the orthorhombic perovskite LaCo1/3Mn2/3O3 as determined by neutron diffraction from 5-300 K. A high-temperature x-ray diffraction study is also reported from 290-900 K. At temperatures above 570 K, LaCo1/3Mn2/3O3 transforms to a rhombohedral structure with space group R3̄c. This rhombohedral phase is also observed in the material at high pressure and the crystal structure has been determined by in situ neutron diffraction at 4.7 GPa. Finally, the ferromagnetic behaviour has been determined by magnetometry and the magnetic structure has been determined using low temperature neutron diffraction at ambient pressure.

A metamolecule antenna for coplanar waveguides.

We report on a metamolecule antenna, based on a fish-scale design but augmented with two split-ring resonators (SRRs) placed within the fish-scale loops. The properties of the antenna resonator, with and without additional SRRs, were examined using finite element method simulations (COMSOL Multiphysics). The simulation findings were subsequently confirmed experimentally, using a vector network analyser coupled to an antenna-loaded coplanar waveguide (CPW). The addition of SRRs to the fish-scale meta-molecule leads to a demonstrably large increase in microwave-absorption. It is shown that the fish-scale/SRR/CPW combination performs as a microwave antenna. Simulations of the antenna gain and far-field emission are presented and discussed.

Switching the in-plane easy axis by ion implantation in rare earth based magnetic films.

Ar(+) ions have been implanted into Laves phase epitaxial thin films of YFe(2) and DyFe(2). Magneto-optical Kerr effect and vibrating sample magnetometry experiments show that the easy and hard axes of magnetization in both materials rotate through an in-plane angle of 90°, whilst the strength of the magnetic anisotropy remains unaltered. This is supported by OOMMF computational modelling. Atomic force microscopy confirms that the film roughness is not affected by implanted ions. X-ray diffraction data show that the lattice parameter expands upon ion implantation, corresponding to a release of strain throughout the entire film following implantation with a critical fluence of 10(17) Ar(+) ions cm(-2). The anisotropy of the films is linked to the strain and from these data it is concluded that the source of anisotropy alters from one where magnetoelastic and magnetocrystalline effects compete to one which is governed solely by magnetocrystalline effects. The ability to locally tune the source of magnetic anisotropy without affecting the film surface and without inducing or eliminating anisotropy could be important in the fabrication of high density magnetic data storage media, spintronic devices and magneto-optical materials.

Some comments on the magnetic moments used in REFe2 exchange spring micro-magnetic simulations.

The current status of magnetic moments used in micro-magnetic modelling of the Laves phase rare earth iron REFe(2) inter-metallic compounds is reviewed. In particular, it is argued that both the neutron scattering results and band structure calculations provide little support for the long-held view that the Fe 3d moments are constant across the REFe(2) series, and for the oft-used rule of thumb that the (57)Fe hyperfine field is proportional to the Fe magnetic moment. Nevertheless, it is argued that it is acceptable to employ a simple ferrimagnetic model, in which the free-ion moment is ascribed to the RE ion and a moment of µ(d) = µ(3d) + µ(5d)≈1.5 µ(B) is used for the combined Fe(3d) and Fe-driven RE(5d) moments.